The invention relates to a radiation emitting device, and more particularly to a system and method for calculating scatter radiation of the radiation emitting device.
Radiation emitting devices are generally known and used, for instance, as radiation therapy devices for the treatment of patients. A radiation therapy device usually includes a gantry which can be swiveled around a horizontal axis of rotation in the course of therapeutic treatment. A linear accelerator is typically located in the gantry for generating a high-energy radiation beam for therapy. This high-energy radiation beam can be an electron radiation or photon (x-ray) beam. During treatment, this radiation beam is typically trained on a zone of a patient lying in the isocenter of the gantry rotation.
In order to provide a proper dose of radiation to a patient, a dose chamber may be used. A dose chamber accumulates dose deliveries from the radiation beam. When the dose of the radiation beam reaches a given number of counts, then the radiation beam may be turned off. The unit with which the dose chamber counts is a xe2x80x9cmonitor unitxe2x80x9d. Determining how many monitor units to set the dose chamber so that the patient receives a proper dose is typically termed as dosimetry. Once a dose for a patient is determined, this dose typically needs to be translated into monitor units. There may be several factors in translating the dose into monitor units, such as attenuation through the patient, accounting for curvature of patient surface, and accounting of scattered radiation inside the patient.
In determining a dose to a patient, a hypothetical plane, often referred to as a calculation plane, a patient plane, or an isocentric plane, directly above the patient may be used in determining the distribution of radiation intensity over the patient. The unit of measurement for radiation intensity is fluence, which is the number of photons per area per time. This calculation plane over the patient may be divided into squares, herein referred to as calculation squares. In determining the fluence over the calculation plane, only one calculation square above the immediate target is typically calculated for the fluence due to the complication of calculating fluence over all of the squares in the calculation plane.
A problem with calculating the fluence in only one calculation square is that the approximation for the remaining calculation squares may be inaccurate. In particular, in the field of intensity modulation, this type of approximation for fluence of the calculation plane may be wholly inadequate. Intensity modulation typically improves the ratio of radiation dose to critical structures versus dose to target. Improving this ratio is highly desirable since it is assumed that non-target areas are receiving radiation. A common goal is to maximize the radiation dose to a target, such as the tumor, while minimizing the radiation dose to healthy tissue.
Another method for calculating the fluence over the calculation plane attempts to calculate the fluence over each calculation square by using ray tracings through a thin aperture. A potential problem with this conventional calculation is that the volume of ray tracing calculations are typically substantial and a substantial amount of processing power is required. Additionally, a radiation aperture, such as a collimator, typically has enough of a thickness to effect the calculations. Accordingly, calculating with the assumption that the aperture is very thin may result in errors.
It would be desirable to have a method for calculating the fluence over the calculation plane which is fast, efficient, and accurate. The present invention addresses such a need.
The present invention relates to an efficient method and system for calculating fluence of a calculation plane over a patient. In one embodiment, a method of the present invention is for calculating fluence contributions for radiation delivery from a source to a treatment area through an aperture. The method includes defining a calculation plane located adjacent to said treatment area and a scattering plane located between the radiation source and the calculation plane. A source plane located between the radiation source and scattering plane is also defined. The method further includes ray tracing a point located on the calculation plane to the scattering plane and projecting the scatter strip from the scattering plane to the source plane to define a rectangular region. An area integration is performed on the rectangular region to determine a fluence value for the element.
In another aspect of the invention, a system generally comprises a processor configured to ray trace a point from a calculation plane located adjacent to said treatment area to a scattering plane to define a plurality of scatter strips, project the scatter strips onto a source plane located between the radiation source and scattering plane to define a plurality of scatter elements corresponding to said plurality of scatter strips, and calculate area integrations for each of said scatter elements. The system further includes a memory coupled with the processor and configured to provide instruction to the processor.
The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages, and embodiments of the invention will be apparent to those skilled in the art from the following description, drawings, and claims.